Traveling with Friend in Europe

My friend and I (both 18yrs and male) are traveling Europe for 10 nights. We are thinking of flying into Amsterdam, then training to Berlin and finishing off with Prague. We are excited to go out at night and meet people, while also experiencing the beauty of these European cities.

I’m curious about

1. What people think about that selection. Are there any cities we should sub in? We are planning on taking trains and staying in hostels.

2. What city we should stay in for the longest? I’ve heard that Berlin is the best for social scene, so should we prioritize spending most time there?